Conservation of structure and mechanism in primary and secondary transporters exemplified by SiaP, a sialic acid binding virulence factor from Haemophilus influenzae

A. Muller, E. Severi, C. Mulligan, A.G. Watts, D.J. Kelly, K.S. Wilson, A.J. Wilkinson, G.H. Thomas

Research output: Contribution to journalArticlepeer-review

Abstract

Extracytoplasmic solute receptors (ESRs) are important components of solute uptake systems in bacteria, having been studied extensively as parts of ATP binding cassette transporters. Herein we report the first crystal structure of an ESR protein from a functionally characterized electrochemical ion gradient-dependent secondary transporter. This protein, SiaP, forms part of a tripartite ATP-independent periplasmic transporter specific for sialic acid in Haemophilus influenzae. Surprisingly, the structure reveals an overall topology similar to ATP binding cassette ESR proteins, which is not apparent from the sequence, demonstrating that primary and secondary transporters can share a common structural component. The structure of SiaP in the presence of the sialic acid analogue 2,3-didehydro-2-deoxyN-acetylneuraminic acid reveals the ligand bound in a deep cavity with its carboxylate group forming a salt bridge with a highly conserved Arg residue. Sialic acid binding, which obeys simple bimolecular association kinetics as determined by stopped-flow fluorescence spectroscopy, is accompanied by domain closure about a hinge region and the kinking of an alpha-helix hinge component. The structure provides insight into the evolution, mechanism, and substrate specificity of ESR-dependent secondary transporters that are widespread in prokaryotes.

Original languageEnglish
Pages (from-to)22212-22222
Number of pages11
JournalJournal of Biological Chemistry
Volume281
Issue number31
DOIs
Publication statusPublished - 4 Aug 2006

Bibliographical note

Copyright © 2006 by the American Society for Biochemistry and Molecular Biology. Uploaded in accordance with the publisher's self-archiving policy.

Keywords

  • CRYSTAL-STRUCTURE
  • RHODOBACTER-CAPSULATUS
  • TRAP TRANSPORTERS
  • LIGAND-BINDING
  • HEMAGGLUTININ-NEURAMINIDASE
  • HALOMONAS-ELONGATA
  • MOLECULAR-GRAPHICS
  • SERUM RESISTANCE
  • SUGAR-BINDING
  • PROTEIN DCTP

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